Pink Underwing Moth (Phyllodes imperialis) - Family: Noctuidae

Pink Underwing Moth - Phyllodes imperialis (Noctuidae)

Final instar Phyllodes imperialis caterpillar.
Recently this spectacular photo has been floating around the internet. I saw it first on Jerry Coyne's "website", then later on Imgur, and then on a crytozoology fact-checking blog called CryptoVille. I have seen a lot of caterpillars with eyespots, but I had never seen this one. This is the caterpillar of a large moth species called the Pink Underwing Moth (Phyllodes imperialis).

The best description of the species I could find comes from an Australian Government website. The Department of Sustainability, Environment, Water, Population and Communities had a Species Profile and Threats Database entry for Pink Underwing Moth (Phyllodes imperialis), where the species has been listed as Endangered. Like most endangered insects the threat is mainly from habitat loss and fragmentation due to logging, agriculture, and other development. Additional information comes from a very useful website on Australian caterpillars (http://lepidoptera.butterflyhouse.com.au/) which is managed by Don Herbison-Evans, and Stella A. Crossley. Unfortunately Stella passed away in 2007, but I have corresponded with Don - he was both enthusiastic and helpful. Finally, I fact-checked these e-resources using the book Moths of Austraila by I.F.B Common. Below I have summarized the reliable information I found about this species.

Species Description

Larva:

Early instars are dull brown, but green individuals are also observed. I'm not sure whether this colour variation is ontological (i.e., changes as the caterpillar ages) or if there are green and brown phenotypes. Later instars have two pairs of distinct eyespots on the anterior end. One pair is on the lateral sides of the first abdominal body segment, while the other pair is concealed under folds of skin.

The caterpillar apparently relies at least in part on crypsis to avoid detection by predators, possibly masquerading as a dried up leaf.

Phyllodes imperialis caterpillar resting on a Carronia multisepalea vine stem
Photo courtesy of plant.nerd. See original photo on Flickr here.
Phyllodes imperialis caterpillar resting on a Carronia multisepalea leaf
Photo courtesy of plant.nerdSee original photo on Flickr here.

However, when the caterpillar feels threatened it rears its anterior body segments, and bends between the first and second abdominal segments. The caterpillar simultaneously curls its real head as well as its true legs underneath the raised portion of its body. By curing in its head and body this way the caterpillar stretches the skin on its dorsal side and reveals the previously-concealed eyespots. These large eyespots are composed of a black pupil surrounded by a blue, then yellow ring (see photos below). Between and below the eyespots are white markings, often described as looking like teeth, and indeed resemble the teeth from a cartoon skeleton. At least 150 people from the Imgur community apparently think it looks like the face of Deadpool especially with the red body depicted in the photo at the top of this post.

This caterpillar is sometimes referred to as the "Big headed caterpillar", the name obviously referring to the appearance of a large false head when the caterpillar adopts this defensive posture. The display likely protects the caterpillar from vertebrate predators (Common 1990). Eyespots and the associated behavioural mimicry that creates a false-head are not uncommon in butterfly and moth caterpillars. Generally it is thought that this suite of traits protects the relatively helpless caterpillars by making them look like a threat (e.g., a snake or other dangerous predator) to an attacker such as an insect-eating bird (Janzen et al 2010).

Phyllodes imperialis caterpillar in defensive posture
Photo courtesy of plant.nerdSee original photo on Flickr here.
Close up of the Phyllodes imperialis caterpillar's eyespots revealed when the caterpillar is threatened
Photo courtesy of plant.nerd. See original photo on Flickr here
Phyllodes imperialis caterpillar in defensive posture
Photo courtesy of plant.nerd. See original photo on Flickr here.
I asked plant.nerd about the caterpillar and how he stimulated the response:
    "These larvae sit flat against the vine like a dead leaf or branch they are very camouflaged and hard to spot. When you place your moving hand close to them or touch them they rear up and bend to reveal the eye spots and the white markings which are usually hidden in a fold of skin."
    • See the full set of plant.nerd's Phyllodes imperialis caterpillar images here.
    The caterpillars feed exclusively on the vines from the Menispermaceae family. In particular the relatively rare vine Carronia multisepalea is reported to be the main food plant. However, other subspecies reportedly feed on Pycanarrhena species of vine (e.g. Pycnarrhena australiana).

    Carronia multisepalea vine the larval host plant of Phyllodes imperialis.
    Photo courtesy of plant.nerd. See original photo on Flickr here.

    Pupa: 

    Many caterpillars change colour at the end of their final larval instar (e.g., Papilio canadensis). This typically coincides with the the end of foraging and beginning of searching for pupation sites. I think this is probably why the caterpillar at the top of this post is red, although spectacular colour morphs are sometimes observed in the caterpillars of other species as well as in other insects (e.g., Pink Katydids). The pupa is about 5 cm long, and is loosely woven into dead leaves on the ground. It is described as bronze in colour, and marked with transparent circumferential panels on the abdominal segments.

    Adult:

    Wingspan listed as 130–140 mm by the Australian Dept. of S.E.W.P.C., but other reports indicate that the size range extends to 170 mm. This discrepancy might indicate that the other populations outside of Australia (Papua New Guinea, Solomon Islands, Vanuatu, and New Caledonia) have larger individuals.

    The "leaf-shaped" forewings are grey-brown and posses a distinctive white marking which seems to vary somewhat among populations. The ventral side of the forewing has a discal, dark-brown coloured patch containing three white spots. The hindwings are dark brown-black with a central patch of pink extending to the inner margin, to which the common name "Pink Underwing Moth" refers. The hindwings are also fringed with 7-8 white lunules on the outer margin. The thorax and abdomen are the same grey-brown colour. A morphologically distinct subspecies of P. imperialis occurs in northern Queensland. The two Australian subspecies are allopatric and the northern subspecies has a larger pink patch on the hindwings.

    Lithograph of an adult Phyllodes imperialis from the Collection of the British Museum
    CATALOGUE OF THE NOCTUIDAE IN THE COLLECTION OF THE BRITISH MUSEUM (1903-1913)
    Sourced from Wikipedia Commons
    Dorsal view of a female Phyllodes imperialis
    Sourced from Wikipedia Commons
    Ventral view of female Phyllodes imperialis
    Sourced from Wikipedia Commons
    Adult Phyllodes imperialis moth from Papua New Guinea. The coin is 3 cm in diameter!
    Photo courtesy of kahunapulej. Original photo can be seen here.
    Adult Phyllodes imperialis held by a little girl named Rachel.
    Photo courtesy of kahunapulejOriginal photo can be seen here.

    Habitat:

    In Australia the moth is only found in undisturbed, subtropical rainforest below the altitude of 600 m. It is tightly associated with the Carronia multisepalea vine. Interestingly, it seems that only when the plant takes the form of a collapsed shrub, and not when it grows in an upright form, does C. multisepalea provide the food and habitat requirements for the moth to breed. As mentioned the moth is also known from Papua New Guinea (incl. the Bismark Archipelago), the Solomon Islands, Vanuatu (New Hebrides), and New Caledonia (Common 1990). The New Caledonia population is apparently considered a distinct subspecies (Common 1990).

    Acknowledgements:

    Both plant.nerd and kahunapulej were very friendly when I contacted them and allowed me to use their spectacular photos for this post. Be sure to check out their photo streams on Flickr:

    References:

    Common, I.F.B. (1990) Moths of Australia. E.J. Brill, New York and Melbourne University Press, Melbourne, Australia. Page 454.

    Department of Sustainability, Environment, Water, Population and Communities (2012). Phyllodes imperialis (southern subsp. - ANIC 3333) in Species Profile and Threats Database, Department of Sustainability, Environment, Water, Population and Communities, Canberra. Available from: http://www.environment.gov.au/sprat. Accessed Mon, 15 Oct 2012 06:04:45 +1100.

    Herbison-Evans, D., Crossley, S. and Moss, J. Lepidoptera Butterflyhouse entry for Phyllodes imperialis.  Updated April 1 2011. http://lepidoptera.butterflyhouse.com.au/cato/imper.html

    Janzen D.H., Hallwachs, W., Burns, J.M. (2010) A tropical horde of counterfeit predator eyes. Proceedings to the National Academy of Sciences 26:11659:11665

    Wikipedia entry for Phyllodes imperialis. http://en.wikipedia.org/wiki/Phyllodes_imperialis Accessed: Oct 20 2012.

    5 comments:

    1. Thank you for the fact checking and the information. I'm not a fan of caterpillars, but this was fascinating.

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    2. This is one beautiful caterpillar. Do you have any idea why it has those white markings? They look like teeth, but I can't think of any animal they would represent. It actually reminds me of a small, angry birdie or a braking gecko...but I guess there isn't any reason to mimic a gecko. So what is it trying to mimic? It doesn't look like any snake or venomous frog.

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    3. Я тоже не любительница гусениц и моли ,но этот вид что то из ряда вон выходящее.Очень интересная информация.Спасибо.

      ReplyDelete
    4. Hi Fracmatic, I don't really know what the white marks are about. I don't suspect teeth mimicry either. I think the most likely explanation is that it simply helps to highlight the scary eye-like markings. As far as the species that is being mimicked I suspect that insect-eating birds are especially afraid of snakes, so anything even vaguely resembling a snake initiates a startle & flee response - a bird that fails to respond to such threats (even when they are sometimes wrong) probably wouldn't survive very long in the natural world. Perfect mimicry probably isn't needed because the birds don't take the time to really look at these guys before they have to make the decision to flee.

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    5. Thank you for replying Thomas! I recently stumbled up on a guess that these marks might simulate a reflection (like that of a snake skin). And you have a great point there-birds do not spend as much time observing caterpillars carefully as we do :D
      You have a wonderful blog with superb information by the way! So keep up the good work and thank you for sharing!

      ReplyDelete